Advise that Approvers cannot approve their own Merge Requests
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### Description
Advise that Approvers cannot approve their own Merge Requests
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Consider a project that has one approver and 1 approve required for each MR.
Once MR creator cant be an approver, MR created by such a user cant be approved by anyone.
What is the possible solution here?
```
### Proposal
Merge Requests approvals can block the Acceptance of a Merge Request indefinitely if a project is set to require approvals, but the only user available to approve the MR is the author of the MR (MR authors cannot approve their own MRs)

Here I am the only collaborator on my project and I have enabled MR approvals functionality. The Merge button is disabled because the MR must be approved but I cannot approve it myself
Add guidance to MR authors to explain this fact when the Accept Merge Request button is disabled.
### Links / references
### Documentation blurb
issue